Multiple record electrologging of wells



Sept. 16, 1941. L. c. BEERS MULTIPLE RECORD ELECTROLOGGING OF WELLSFiled March 8, 1939 Sheets-Sheet l 11v VENTOR LOWELL C. BEE/F's Mm}Patented Sept. 16, 1941 MULTIPLE RECORD ELECTROLOGGING OF WELLS LowellC. Beers, Los Angeles, Calif., assignor to Lane-Wells Company, LosAngeles, Calif., a corporation of Delaware Application March 8, 1939,Serial No. 260,593

3 Claims.

My invention relates to multiple record electrologging of wells. Anaccepted present method of electrologging, that is, electricalinvestigation of formation traversed by a well-bore, employs an inputcircuit and a probe circuit terminating in four electrodes suspendedfrom av multiple conductor cable. One electrode of the input circuit, aswell as one of the electrodes of the probe circuit, may be'the sheath ofthe cable itself, or the well casing above the region to be surveyed, ora surface ground. Electrical energy is supplied preferably to thelowermost electrode and to the sheath of the conductor, or casing, orupper electrode, or surface ground, as the case may be. The remainingtwo electrodes serve as probe electrodes. In practice, three, andsometimes four, curves or graphs are obtained by means of the electrodesand their associated electrical apparatus at the surface.

FirstShalZow 1esistivity.--This is measured in the input circuit acrossthe two input electrodes. If one of the electrodes, such as the easingor cable sheath, is of large area, the measurement obtained is largelythat of the fluids in proximity to the other, or smaller, input elec-=trode, due to the fact that the current density is greatest adjacent thesmall electrode.

Second-Natural or spontaneous potential, or

porosity.-This is measured also between. the two input electrodes, butwithout artificial current flowing in the circuit, so that the resultingvoltage fluctuations in the circuit are due solely to the effect of theelectrolyte present in the formation, in proximity to the well-bore.

Third-Deep resistivity.--'Ihis is the resistivity, or averageresistivity, existing at a predetermined distance from the smaller inputelectrode. This is measured by means of two probe electrodes whichrequire, in the conventional apparatus, two conductors leading to thesurface, or one probe electrode and cable sheath with one extraconductor to the surface.

Among the objects of my invention are:

First, to provide a process and apparatus whereby the first, or shallowresistivity curve, and the second, or spontaneous potential curve, maybe obtained with a single conductor cable during one trip into or out ofa well-bore;

Second, to provide a process and apparatus of this character which isparticularly designed for operation in conjunction with the process andapparatus for obtaining simultaneously the first curve and the third, ordeep resistivity curve, such other process and apparatus being disclosedin the copending application, Serial No. 254,639,

filed February 4, 1939, thus providing a process and apparatus which,when incorporated with that of said copending application, enables theproduction of all three curves with only a single trip into a well-boreand without the use of a multiple conductor cable;

Third, to provide a process and apparatus of this character wherein thefirst and second curves are taken in alternation, thereby minimizing theinterference between the two circuits employed in order to obtain thecurves;

Fourth, to provide a process and apparatus of this character wherein,without increasing the number of conductors in the cable, the circuitsfrom which the first and second curves are derived may utilize separateelectrodes or identical electrodes, as desired;

Fifth, to provide an apparatus of this character -.wherein thoseelements of the apparatus suspended from the cable and in immediateassociation with the electrodes may be extremely simple and compact, andfully capable of withstanding the extreme conditions of heat andpressure, as well as mechanical jarring or im pacting encountered whenlowered into a well bore;-and

Sixth, to provide an apparatus of this characterwherein a particularlysimple and direct circuit is provided for the measurement of spontaneouspotentials so that variations in the potentials measured, which areactually very weak, may be measured with high facility and with aminimum loss in transmission;

With the above and other objects in view, as will appear hereinafter,reference is directed to the drawings, in which:

Figure 1 is a wiring diagram illustrating my apparatus;

Figure 2 is a fragmentary wiring diagram of that portion of theapparatus associated with the electrodes, showing a modified formthereof;

Figure 3 is another wiring diagram of a further modified form of theapparatus associated with the electrodes; and

Figure 4 is a wiring diagram illustrating a further modification whereinfour curves may be produced.

Reference is first directed to Figure 1: A single conductor cable II isemployed which comprises a metallic sheath l2 and a single conductor I3.The sheath I2 serves both as a conductor and as one of the electrodes,inasmuch as this member is grounded. The lower end of the cable supportsan electrode assembly, designated generally by l4. The conductor I3 isconnected through a solenoid coil I of a relay I6 to a condenser I1 andan input electrode l8,

which serves to measure both shallow resistivity and natural potentials,as will be explained here- The solenoid I5 operates a single contactswitch I9 which, when closed, shorts out the inafter.

. condenser l1. This switch'normally occupies a closed position and isheld open only when the solenoid I5 is energized and current is flowingin'the conductor I3 from an artificial source of supply.

The electrode assembly incorporates two probe electrodes 29 and 2| whichare connected through condensers 22 and 23, respectively, to thealternating current side of a rectifier 24. The direct 1 current side ofsaid rectifier is connected by a I lead 25 to the cable sheath 82 bylead 26 through 1 an alternating current filter 21 to the conductor II3. The'probe electrodes 29 and 29, and their associated circuits, are"employed to measure deep resistivity, that is, to derive the thirdcurve, I and, except for its combination with the elements of my processand apparatus, is the invention embraced in the aforementioned copendingslip rings 35, 36 and 31. slip ring 31 is connected by a lead 33 to asuit- 2 I able recording galvanometer 39, the other end of 36 and 31,each of which, for convenience, are shown as coacting with a pair ofbrushes to complete and break circuits therethrough. The conductor I3 isconnected to brushes which ride on The other brush of which is connectedby a lead 40 to ground so that galvanometer 39 records the second curve.The other brush of slip ring 36 is connected i throughlead 4| to analternating current filter 62, then to a recording galvanometer 43 whichrecords the third curve. The other side of the galvanometer is connectedto the lead 40.-

The slip ring 35 connects, through a condenser 1 44, to an alternatingcurrent bridge 45, the other terminal of which is joined to the groundlead 49. The .alternating current bridge 45 is prociated with slip ring33 which, in turn, is connected with a source of alternating current 41.The other side of the alternating current 41' is 1 connected to a slipring 34, which is likewise connected to the ground lead 40.

A recording galvanometer 48 for the recording of the first curve isconnected with the alternatthe alternating current source is connectedto the ground lead 40 and to the bridge 45, one leg of which comprisesthe circuit through the conductor I3 and sheath I2. Consequently,alterhating current, through condenser I1, is applied to the inputelectrode I8 and sheath I2 as. the

,other input electrode, so as'to establish an alterhating current fieldtherebetween. By reason of the fact that the sheath I2 ofthe cable has arelatively great area, the current density is very low, whereas thecurrent density in immediate proximity to the electrode I8 is very high.As a result, the resistance of the circuit formed with the bridge 455 isparticularly influenced by the resistivity of the fluids in closeproximity to the electrode I3. This variation in resistance is measuredby the galvanometer t3 connected with the bridge 65. Simultaneouslytherewith the probe electrodes 29 and ti sample the field establishedbetween electrode l8 and the sheath i2. The electrical values obtainedby these electrodes 2i? and El are essentially that of the potentialvided with a lead at extending to a brush assoing current bridge 45,preferably through a meter rectifier 49 which, incidentally, may besimilar i to the rectifier 24 and permits the use of a direct currentmeter corresponding to meters 39 and :43 which are also direct-currentoperated.

Operation of my circuit is as follows: For onehalf the cycle vofoperation the first and third curves are produced. During the other halfof the cycle of operation the second curve is made. The cycle ofoperation of my apparatus is ,preferably materially less than thefrequency of the alternating current source 41; for example, if thealternating frequency source is cycles per sec- .ond, the frequencycycles of the slip rings driven by the motor 32 may be ten per second;if a higher alternating current source frequency is used it follows, ofcourse, that the cycle of my [apparatus may be increasedcorrespondingly.

During the one-half cycle of operation in which the first and thirdcurves are being measured difference between equi-potential surfacesestablished with the electrode I8 as the center, one having a boundarydefined by the position of electrode 2t and the other having a boundarydefined by the position of electrode ill. The alternating current set upby the alternating potential sampled by the electrodes 20 and ii isrectified and fed into the conductor I3 as direct current between thecondensers I1 and M, and by reason of these condensers, as well ascondensers 22 and 23, such rectified current cannot find its way backinto the formation, or be affected by any direct current field existingin the formation. Such rectified direct current is fed to thegalvanometer 43 to form the third curve. The alternating current filters2-1 and 42 prevent alternating current'from the source 51 from findingits way into the direct current circuit established between therectifier 24 and the galvanometer $3, unless such alternating current ispicked up by the electrodes 20 and 2I; and, therefore, is representativeof the alternating current field established by the input electrodes.The operation and inter-relation of electrodes I8, 20 and 2|, in thisrespect, is more particularly set forth in the cbpending applicationhereinbefore referred to.

During the other half cycle of operation, the alternating current supply41 is opened, as well as the circuits through slip rings 35 and 36. iThe conductor I3 is connected, through slip ring 31, directly togalvanometer 39, and thence to ground 40. When this condition obtains,solenoid I5 of the relay switch I6 is de-energized, contacts I9 areclosed, shorting condensers I1; and consequently, the only source ofcurrent flow in the circuit is due to the natural potentials, orspontaneous potentials, as they are sometimes called, existing in theformation and which bear a relation to the porosity of the formation, ashas been well established in the art of electrologging.

The frequency of change-over from one circuit to the other and the typeof galvanometer used are chosen so that the resulting curve will appearcontinuous, that is, the galvanometers are damped to carry them over'their idle period.

Thus, by first opening and then shorting condensers I1, and at the sametime connecting and disconnecting the source of alternating-current,

it is possible to obtain the first and second curves trode 18, eitherelectrode or 2| may be substituted. Furthermore, it is possible, and insome instances preferable,- to employ a separate electrode for thepurpose of measuring natural or spontaneous potentials. This is done byrunning a lead 5| from the switch If! to an electrode 52 which may bemounted anywhere in the electrode assembly, but preferably in closeproximity to electrode I8, all of which is shown best in Figure 2. Theremaining parts of the electrode assembly are similar to thosepreviously described.

Reference is now made to Figure 3, in which is illustrated a modifiedform wherein one of the probe electrodes is made common with the sheathI2 of the cable. This is accomplished by merely interposing thecondenser 23 in the lead extending to the sheath l2 of the cable.Otherwise the circuit shown in Figure 3 may be similar to that shown inFigure 1 or 2.

It should be borne in mind that the art of electrologging has been wellestablished and that the use of the cable 'sheath both as one or more ofthe electrodes, as well as the conductor, has been well established. Inother words, it is well known in the art to measure by means of atwo-conductor cable and two electrodes corresponding to electrodes l8and 20, utilizing the sheath of the cable as both a probe and inputelectrode, as well as conductor. Similarly, it has been customary to usethe equivalent of electrodes I8, 20 and 2| in association with athreeconductor cable and its sheath. Still further, it has been commonpractice to use four'electrodes; in other words, making the second inputelectrode independent of the sheath, this, of course, requiring fourconductors instead of three or two. Therefore, the term electrodeincludes the sheath insofar as it functions as the electrode, and theterm conductor likewise includes the sheath insofar as it functions as aconductor.

A fourth curve is sometimes plotted in conventional electrolog practice,either in addition to or in substitution of the third curve. Such afourth curve is, in efiect, a combination of the second, or spontaneouspotential curve, and the third, or deep resistivity curve, and,preferably, is obtained between a probe electrode and the sheath of thecable, or other elongated electrode, while the input circuit is inoperation, but without means in the probe circuit for filtering out anydirect current that may be present naturally in .the formation. Suchfourth curve isv obtained, in conventional practice, whether the inputcircuit is direct current or alternating current.

It is possible to obtain such fourth curve in conjunction with myspecial arrangement, as indicated in Figure 4. In many respects thecircuits shown in Figure 4 are similar to those shown in Figures 1, 2and 3, and those parts which correspond to the elements in Figures 1, 2and 3 bear the same reference characters. It is preferable to use thetwo-electrode system, that is, a single input electrode l8 and probeelectrode 20 similar to that shown in Figure 3, the sheath l2 of thecable serving as a conductor as well as probe and input electrode.

A time-delay relay switch II is provided in the electrodev assembly I2at the lower end of the cable II. The time-delay switch ll includes asolenoid I3 and a thermostatic or other de'ayaction element 14 connectedin series with each other across the conductor l3 and cable sheath l2.opened when the thermal element 14 has been energized a predeterminedinterval, thereby breaking the circuit to the solenoid 13 even thoughthe input circuit is closed. .The solenoid 13 controls a pair ofcontacts 16 which are adapted, when closed, to short out the condenser22 associated with probe electrode 20.

At the surface, an interrupter 8| is provided which is represented ascomprising a motor 82 which drives a series of contact rings 83, 85, 8B,81 and 88. The contactor rings are divided'into thirds so that there arethree periods to each cycle of operation. The contactor ring 83corresponds to contactor ring 33 in that it connects the source ofalternating current 41 with the lead no contactor ring corresponding toring 34 in Figure 1 is necessary.

Contactor ring 85 corresponds to contactor ring 35 and is connectedthrough condenser 44 to one leg of the bridge and to the conductor l3.Similarly, contactor ring 81 corresponds to contactor ring 31 andconnects the conductor l3 with lead 38 to recording galvanometer 39,which produces the second curve.

Contactor ring 85, which corresponds to contactor ring 36, and an addedcontactor ring 88, are connected to the conductor 13 through analternating current filter 42 and to leads 4| and 89, respectively,which connect to recording galvanometers 43 and 90, respectively,adapted to produce the third and fourth curves.

In this connection, it should be noted that the circuit to the recordinggalvanometer 43 is similar to that shown in Figure 1, except that the 1alternating current filter 42 is placed between vanometer 43, inasmuchas the filter is needed for recording galvanometer 90.

Operation of the circuit shown in Figure 4 is as follows: Thealternating current source is connected in the input circuit for twoperiods of the cycle. However, the time-delay switch II is so arrangedthat switch 16 remains open only during the first period of the cycle.During the first period of the cycle the recording galvanometer 43 is inoperation, producing the third curve. During the second period of thecycle, when the switch 16 is closed the condenser 22 is'shorted andrecording galvanometer is connected by reason of its slip ring 88, sothat both the spontaneous potentials and. the alternating current fieldestablished between the electrode l8 and sheath l2 are picked up. Itshould be noted that the direct current resulting from the spontaneouspotentials passes readily through the rectifier and alternating currentfilter, and the alternating current which is picked up is firstrectified and then passed through the filter, so that both are deliveredto the galvanometer 9|! as direct current.

' During both the first and second periods, the

galvanometer 48, which plots the first curve, may be in operation.During the third period of operation, switch I6 is still closed, but nocurrent is flowing in the input circuit, so that electrode 20 isresponsive to spontaneous potentials only and these are measured by therecording galvanometer 39, this being the only galvanometer nowconnected in the circuit.

It should be noted that inasmuch as solenoid l3 and element 14constitute a; drain on the al- A pair of contacts 15 are adapted to'beternating current source, a dummy load may be substituted in thiscircuit during the second period, when switch 15 is open. Such auxiliarydevices are, of course, contemplated, but for simplicity of illustrationare omitted from the diagrams.

Varlousphanges and alternate arrangements may be made within the scopeofthe appended claims, in which it is my intention to claim all noveltyinherent in the apparatus and processes as broadly as the prior artpermits.

I claim: 1. A method of measuring a plurality of electricalcharacteristics of formation confronting a well-bore and transmittingthe same to the top of the well-bore, characterized by: establishing byan input circuit an electrical field in the formation between a pair ofelectrodes; measuring in the input circuit the electrical properties ofthe formation more remote from said' electrodes; con-' verting thecurrent as'sampled to a current dissaid electrical field; and measuringthe natural potential present at said electrodes when said electricalfield is interrupted.

2. An apparatus for electrologging wells, comprising: a pair ofelectrodes adapted to be.

suspended in a well-bore in electrical association with formationtraversed by said well-bore; an

input circuit for establishing periodically an artificial electricalfield through formation between said electrodes; means for measuringsaid artificial electrical field when said circuit is in operation; andmeans for measuring the natural elec- 'trical potential present in theformation when 3. An apparatus as set forth in claim 2 wherein I saidinput circuit is provided with an alternating current source whereby analternating current field is established and wherein the period ofoperation and non-operation of said circuit have durations of at leastseveral cycles of said alter-

